U.S. patent application number 15/241810 was filed with the patent office on 2017-11-30 for fabrication of m-plane gallium nitride.
The applicant listed for this patent is NATIONAL SUN YAT-SEN UNIVERSITY. Invention is credited to I-Kai Lo, Jenn-Kai Tsai, Shuo-Ting You.
Application Number | 20170345650 15/241810 |
Document ID | / |
Family ID | 59367340 |
Filed Date | 2017-11-30 |
United States Patent
Application |
20170345650 |
Kind Code |
A1 |
Lo; I-Kai ; et al. |
November 30, 2017 |
Fabrication of M-plane Gallium Nitride
Abstract
The present disclosure provides a fabrication of M-plane gallium
nitride which is able to grow M-plane gallium nitride without the
need of expensive substrates, such as LiAlO.sub.2, LiGaO.sub.2 or
SiC. The fabrication of M-plane gallium nitride includes preparing
a zinc oxide hexagonal prism having a growth face, and growing a
gallium nitride layer on the growth face of the zinc oxide
hexagonal prism. The growth face is an M-plane perpendicular to a
direction of gravity.
Inventors: |
Lo; I-Kai; (Kaohsiung,
TW) ; You; Shuo-Ting; (Kaohsiung, TW) ; Tsai;
Jenn-Kai; (Kaohsiung, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NATIONAL SUN YAT-SEN UNIVERSITY |
Kaohsiung |
|
TW |
|
|
Family ID: |
59367340 |
Appl. No.: |
15/241810 |
Filed: |
August 19, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 21/02513 20130101;
H01L 21/02472 20130101; H01L 21/02647 20130101; H01L 21/02631
20130101; H01L 21/02554 20130101; H01L 21/0254 20130101; H01L
21/02609 20130101; H01L 21/02516 20130101; H01L 21/02628 20130101;
H01L 21/02381 20130101; H01L 21/02389 20130101 |
International
Class: |
H01L 21/02 20060101
H01L021/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 31, 2016 |
TW |
105117061 |
Claims
1. A fabrication of M-plane gallium nitride, comprising: preparing
a zinc oxide hexagonal prism having a growth face, wherein the
growth face is an M-plane perpendicular to a direction of gravity;
and growing a gallium nitride layer on the growth face of the zinc
oxide hexagonal prism.
2. The fabrication of M-plane gallium nitride as claimed in claim
1, wherein the zinc oxide hexagonal prism has a height of 1-3 .mu.m
and a diameter of 1-2 .mu.m.
3. The fabrication of M-plane gallium nitride as claimed in claim
1, wherein the gallium nitride layer is grown by plasma-assisted
molecular beam epitaxy.
4. The fabrication of M-plane gallium nitride as claimed in claim
3, wherein the gallium nitride layer is grown at 500-600.degree.
C.
5. The fabrication of M-plane gallium nitride as claimed in claim
4, wherein the gallium nitride layer is grown at 550.degree. C.
6. The fabrication of M-plane gallium nitride as claimed in claim
3, wherein the gallium nitride layer is grown with an N/Ga flux
ratio of 40-60.
7. The fabrication of M-plane gallium nitride as claimed in claim
6, wherein the gallium nitride is grown with an N/Ga flux ratio of
53.
8. The fabrication of M-plane gallium nitride as claimed in claim
1, wherein preparing the zinc oxide hexagonal prism includes
preparing a base plate and growing the zinc oxide hexagonal prism
on a surface of the base plate by hydrothermal reaction.
9. The fabrication of M-plane gallium nitride as claimed in claim
8, wherein the base plate is a Si(100) base plate.
10. The fabrication of M-plane gallium nitride as claimed in claim
8, wherein a reaction solution used in the hydrothermal reaction
includes zinc nitrate hexahydrate and hex amethylenetetramine.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The application claims the benefit of Taiwan application
serial No. 105117061, filed on May 31, 2016, and the subject matter
of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention generally relates to a fabrication of
gallium nitride and, more particularly, to a fabrication of M-plane
gallium nitride.
2. Description of the Related Art
[0003] c-plane gallium nitride is widely used in the light emitting
diode. However, due to quantum confined Stark effect, c-plane
gallium nitride is provided with reduced luminous efficiency.
Replacing c-plane gallium nitride with M-plane gallium nitride may
overcome the above problem, thus improving luminous efficiency. A
conventional fabrication of M-plane gallium nitride uses
LiAlO.sub.2, LiGaO.sub.2 or SiC as a substrate for growing M-plane
gallium nitride thereon. However, production of these substrates is
complicated with high cost, resulting in high production cost of
M-plane gallium nitride.
[0004] In light of the above, such a conventional fabrication of
M-plane gallium nitride still needs improvement.
SUMMARY OF THE INVENTION
[0005] It is therefore the objective of this invention to provide a
fabrication of M-plane gallium nitride which is able to grow
M-plane gallium nitride without the need of expensive substrates,
such as LiAlO.sub.2, LiGaO.sub.2 or SiC.
[0006] The present disclosure provides a fabrication of M-plane
gallium nitride, including: preparing a zinc oxide hexagonal prism
having a growth face, and growing a gallium nitride layer on the
growth face of the zinc oxide hexagonal prism. The growth face is
an M-plane perpendicular to a direction of gravity.
[0007] The fabrication of M-plane gallium nitride in the present
disclosure can grow M-plane gallium nitride without the need of the
expensive substrates such as LiAlO.sub.2, LiGaO.sub.2 or SiC. The
fabrication of M-plane gallium nitride is provided with simple
steps and low cost, thus reducing the production cost of the
gallium nitride layer.
[0008] In a form shown, the zinc oxide hexagonal prism has a height
of 1-3 .mu.m and a diameter of 1-2 .mu.m. As such, the growth face
is provided with a fine quality, thus assuring the quality of the
fabricated gallium nitride layer.
[0009] In the form shown, the gallium nitride layer is grown by
plasma-assisted molecular beam epitaxy. The gallium nitride layer
is grown at 500-600.degree. C., or at 550.degree. C. The gallium
nitride layer is grown with an N/Ga flux ratio of 40-60, or with an
N/Ga flux ratio 53. As such, lattice defect can be prevented, thus
improving illuminating efficiency of the gallium nitride.
[0010] In the form shown, preparing the zinc oxide hexagonal prism
includes preparing a base plate and growing the zinc oxide
hexagonal prism on a surface of the base plate by hydrothermal
reaction. The base plate is a Si(100) base plate. A reaction
solution used in the hydrothermal reaction includes zinc nitrate
hexahydrate and hexamethylenetetramine. As such, the zinc oxide
hexagonal prism can be provided with high quality and low
production cost.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The present invention will become more fully understood from
the detailed description given hereinafter and the accompanying
drawings which are given by way of illustration only, and thus are
not limitative of the present invention, and wherein:
[0012] FIG. 1 is a flow chart of a fabrication of M-plane gallium
nitride according to the present disclosure.
[0013] FIG. 2 is a ball stick model at an interface between zinc
oxide and gallium nitride.
[0014] FIG. 3a is an XRD result of zinc oxide hexagonal prisms.
[0015] FIG. 3b is a SEM image of the zinc oxide hexagonal
prisms.
[0016] FIG. 3c is an enlarged SEM image of one of the zinc oxide
hexagonal prisms.
[0017] FIG. 4a is a SEM image of a gallium nitride layer.
[0018] FIG. 4b is an enlarged SEM image of the gallium nitride
layer.
[0019] FIG. 5a is a TEM image of the zinc oxide hexagonal prism and
the gallium nitride layer.
[0020] FIG. 5b is a SAD pattern of the gallium nitride layer.
[0021] FIG. 5c is a SAD pattern of the interface between the
gallium nitride layer and the zinc oxide hexagonal prism.
[0022] FIG. 5d is a SAD pattern of the zinc oxide hexagonal
prism.
[0023] FIG. 6 is a polarization-dependent PL spectra of the gallium
nitride layer and the zinc oxide hexagonal prism.
[0024] In the various figures of the drawings, the same numerals
designate the same or similar parts. Furthermore, when the terms
"first", "second", "third", "fourth", "inner", "outer", "top",
"bottom", "front", "rear" and similar terms are used hereinafter,
it should be understood that these terms have reference only to the
structure shown in the drawings as it would appear to a person
viewing the drawings, and are utilized only to facilitate
describing the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0025] With reference to FIG. 1, a fabrication of M-plane gallium
nitride according to the present disclosure may include a zinc
oxide preparation step S1 and a gallium nitride growth step S2. The
zinc oxide preparation step S1 my include preparing a zinc oxide
hexagonal prism having a growth face, with the growth face being an
M-plane perpendicular to a direction of gravity. The gallium
nitride growth step S2 may include growing a gallium nitride layer
on the growth face of the zinc oxide hexagonal prism.
[0026] The term "M-plane gallium nitride" used hereinafter in the
specification refers to gallium nitride with a growth direction of
[1010]. Specifically, the gallium nitride layer can grow on the
growth face in a manner of M-plane stacking, such that the gallium
nitride possesses M-plane characteristics.
[0027] The preparation of the zinc oxide hexagonal prism is not
limited in the present disclosure. For instance, the zinc oxide
hexagonal prism can be prepared by hydrothermal method on a surface
of a base plate. The size of the zinc oxide hexagonal prism is
preferably micrometer-scale, e.g. a height of said prism can be 1-3
.mu.m, and a diameter (i.e. maximal length of the base face) of
said prism can be 1-2 .mu.m. As such, the growth face is provided
with a fine quality, thus assuring the quality of the fabricated
gallium nitride layer. In the present embodiment, on a surface of a
Si(100) base plate, zinc nitrate hexahydrate and
hexamethylenetetramine are used as reacting agents to conduct
hydrothermal reaction at 70-100.degree. C. for 10-20 hours, so as
to grow the zinc oxide hexagonal prism on the Si(100) base
plate.
[0028] The zinc oxide hexagonal prism is adapted for providing the
growth face on which the gallium nitride layer grows. Specifically,
the zinc oxide hexagonal prism has two base faces and six side
faces, with each side face being M-plane. The zinc oxide hexagonal
prism lays down with one of its M-plane perpendicular to the
direction of gravity to serve as the growth face. In the present
embodiment, the zinc oxide hexagonal prism has one of its M-plane
adheres to the surface of the base plate, with an opposite one of
its M-plane serving as the growth surface.
[0029] Before growing the gallium nitride, a pretreatment can be
conducted to remove water and organic pollutions of the zinc oxide
hexagonal prism, and to anneal the zinc oxide hexagonal prism.
Specifically, in the present embodiment, the zinc oxide hexagonal
prism (with the base plate) is dried at 180.degree. C. under a
vacuum of 10.sup.-7-10.sup.-8 torr. Organic pollutions of the zinc
oxide hexagonal prism are removed at 550.degree. C. under a vacuum
of 10.sup.-9 torr. Finally, the zinc oxide hexagonal prism is
annealed at 600-650.degree. C. under a vacuum of 10.sup.-10 torr,
providing an appropriate environment for growing the gallium
nitride layer.
[0030] The gallium nitride layer can be grown by magnetron
sputtering, atomic layer deposition, pulse laser deposition, and
etc. Or, the gallium nitride layer can be grown by molecular beam
epitaxy under a low-temperature environment. In the present
embodiment, the gallium nitride layer is grown by plasma-assisted
molecular beam epitaxy at 500-600.degree. C. under a low N/Ga ratio
(vapor pressure of N/vapor pressure of Ga) environment. For
instance, the N/Ga flux ratio can be of 40-60, preferably set at
53; the growth time can be 30 min to 3 hr, preferably set at 1 hr,
for producing the gallium nitride layer with less lattice defects.
After growing the gallium nitride layer, the gallium nitride layer
can be lifted off from the zinc oxide hexagonal prism by laser
lift-off process. During the process of plasma-assisted molecular
beam epitaxy, a high environmental temperature may cause
dissociation of zinc oxide which reacts with nitrogen or gallium,
resulting in stacking fault of the gallium nitride layer.
[0031] It is noteworthy that the lattice parameters of zinc oxide
are a=3.25 .ANG. and c=5.2 .ANG., which are very close to that of
gallium nitride (3.20 .ANG. and 5.18 .ANG.), and the
lattice-mismatch level of zinc oxide and gallium nitride is quite
low (lattice-mismatches of [1120].sub.ZnO//[1120].sub.GaN and
[0002].sub.ZnO//[0002].sub.GaN are 1.86% and 0.6%, respectively).
Hence, with references to FIG. 2, in the a-axis direction A,
a.sub.ZnO.apprxeq.a.sub.GaN; and in the c-axis direction C,
c.sub.ZnO.apprxeq.c.sub.GaN. Accordingly, zinc oxide can be an
appropriate substrate for growing M-plane gallium oxide thereon.
Moreover, when growing the gallium nitride layer, the nitrogen
source and the gallium source descend in the gravity direction to
grow gallium nitride. Therefore, the growth face of the zinc oxide
hexagonal prism must be perpendicular to the direction of gravity,
such that the nitrogen and gallium sources can be deposited on the
growth face to grow the gallium nitride layer upwardly from the
M-plane of the zinc oxide hexagonal prism, forming M-plane gallium
nitride. In contrast, if the zinc oxide hexagonal prism stands with
one of its base faces adhering to the base plate and with its
M-planes parallel to the gravity direction, only a small part of
the nitrogen and gallium source can adhere on the M-plane of the
zinc oxide hexagonal prism for growing M-plane gallium nitride.
Thus, most of the nitrogen and gallium sources are deposited on the
surface of the base plate instead of the M-plane. Gallium nitride
which is not M-plane characterized may thus grow on the surface of
the base plate and may adversely affect the growth of the gallium
nitride layer growing on the growth face of the zinc oxide
hexagonal prism.
[0032] For proving the ability of the fabrication of M-plane
gallium nitride to grow gallium nitride layer which is M-plane, the
following experiments are carried out.
[0033] In this experiment, the zinc oxide hexagonal prism is grown
on a Si(100) base plate by hydrothermal method at 90.degree. C. for
60 min, with the reaction solution including 0.15 M zinc nitrate
hexahydrate and 0.03 M hexamethylenetetramine. The zinc oxide
hexagonal prism obtained is analyzed: the XRD result is shown in
FIG. 3a, and the SEM images are shown in FIGS. 3b and 3c. These
results show that the zinc oxide hexagonal prism having smooth
M-plane can be prepared by hydrothermal method. Such a smooth
M-plane can be adapted for the gallium nitride layer to grow
thereon.
[0034] Next, the gallium nitride layer is grown on the growth face
of the zinc oxide hexagonal prism by plasma-assisted molecular beam
epitaxy at 550.degree. C. for 60 min, with an N/Ga flux ratio of
53. The SEM images of the gallium nitride layer obtained are shown
in FIGS. 4a and 4b. The zinc oxide hexagonal prism with M-plane
gallium nitride is further analyzed by TEM and SAD, and the results
are shown in FIGS. 5a-5d. FIG. 5a shows the cross sectional TEM
image along [1010] direction; FIGS. 5b-5d are the SAD patterns
taken at location DP01, DP02 and DP03 indicated in FIG. 5a. With
references to FIG. 5b, the gallium nitride layer shows wurtzite
structure with a growth direction of [1010]. With references to
FIG. 5d, the zinc oxide hexagonal prism shows M-plane wurtzite
structure. With references to FIG. 5c, the SAD patterns of the
gallium nitride layer and the zinc oxide hexagonal prism overlap at
location DP02, indicating the diffraction spots of
GaN(1120)//ZnO(1120), thus proving that the gallium nitride layer
is gown with [1010] direction parallel to ZnO[1010].
[0035] Furthermore, the zinc oxide hexagonal prism and M-plane
gallium nitride are analyzed by polarization-dependent
photoluminescence under room temperature, and the result is shown
in FIG. 6. In this polarization-dependent PL spectra,
.phi.=0.degree. is defined parallel to c-axis. The intensity of PL
spectra increased from .phi.=0.degree. (E//c) to .phi.=90.degree.
(E.perp.c), indicating the characteristic of nonpolar plane GaN and
ZnO, which also proves that the gallium nitride layer is
M-plane.
[0036] According to the above, by using the zinc oxide hexagonal
prism as a substrate, the fabrication of M-plane gallium nitride in
the present disclosure can grow M-plane gallium nitride without the
need of the expensive substrates such as LiAlO.sub.2, LiGaO.sub.2
or SiC. The fabrication of M-plane gallium nitride is provided with
simple steps and low cost, thus reducing the production cost of the
gallium nitride layer.
[0037] Moreover, in the fabrication of M-plane gallium nitride of
the present disclosure, the gallium nitride layer is grown on the
growth surface of the zinc oxide hexagonal prism. Since the growth
surface is an M-plane perpendicular to the direction of gravity,
the gallium nitride layer can certainly form M-plane gallium
nitride with less lattice defects, thus improving luminous
efficiency of the gallium nitride layer.
[0038] Although the invention has been described in detail with
reference to its presently preferable embodiments, it will be
understood by one of ordinary skill in the art that various
modifications can be made without departing from the spirit and the
scope of the invention, as set forth in the appended claims.
* * * * *